The present invention relates to a phase detection method and a processor for determining a phase of a receiving signal based on a plurality of consecutive values of a receiving signal.
Exactly determining the phase of an output signal at the outlet of a transferring medium when being stimulated by an input signal of a known frequency at the inlet is of great importance for a number of applications. The phase information in coding methods in communications engineering can, for example, be used for transmitting communications in the form of electric, magnetic or electromagnetic signals via a communications channel. In the area of materials sciences, measuring the phase of an acoustic wave provides information on the material composition of the transferring medium. In chemical and physical analyzing systems, phase detectors are used for determining temperature, density, phase changes in chemical reactions, object dimensions and concentration of liquids in chemical and physical media. In medical diagnostic methods, tissue characteristics are identified by measuring the phase of acoustic and ultrasonic signals being coupled in. Applications for these purposes include monitoring blood circulation in the body in order to recognize abnormal conditions, in particular in the brain, and mammary sonography.
FIG. 1 shows a schematic view of a system 100 for measuring phase relations of acoustic waves in a vessel 102. The system 100 comprises a vessel 102 which is to be measured, e.g. a body cell, a blood vessel or an artery having a vessel length L and a transmitter 101 and a receiver 103 of ultrasonic waves. The transmitter 101 couples an ultrasonic wave 104 of a known frequency f0 comprising a phase φ0 into the vessel 102 at the inlet 105 of the vessel 102, where said ultrasonic wave 104 spreads and is received at the outlet 107 by the receiver 103. As can be seen in FIG. 1, the ultrasonic wave 104 comprises an integer number of oscillatory periods P as well as a partial period, which can be represented as a phase difference φ1−φ0. Between the running time Tp the acoustic wave 104 and the phase difference φ1−φ0, the following condition applies:2π·f0TP=2πP+(φ1−φ0).  (1)
For the phase velocity V in the vessel 102, the following condition applies on the one hand:V=λ·f0,  (2)wherein f0 denotes the known transmitting frequency and λ denotes the wave length in the vessel 102. On the other hand, the following condition applies for the phase velocity V in the vessel 102:
                              V          =                                    K              ρ                                      ,                            (        3        )            wherein K denotes the elasticity of the vessel and ρ denotes its density. The characteristics of the vessel 102 can therefore be determined from the phase velocity V. The wave length λ can be determined from the amount of periods P and from the phase difference φ1−φ0, and the phase velocity V can be identified by means of the known transmitting frequency f0, the material characteristics of the vessel 102 being able to be characterized by means of the phase velocity V.
Generally, the receiver is synchronized with the transmitter in order to determine the phase difference φ1−φ0 and the received signal is sampled with an analog-to-digital converter. The sampling value of the received signal can be correlated with the point of time of synchronization from which the phase difference can be determined.
However, the measuring accuracy depends on a plurality of system parameters, such as the sampling accuracy, the accuracy of the set frequency of the transmitting signal, the coupling and uncoupling accuracy of the acoustic signal, interferences of the transmitting signal due to reflections at the vessel ends and vessel walls, Doppler effects, etc.